Though many drugs are widely used for illicit purposes, comparatively little is known about the ways in which development and loss of tolerance may differ for different classes of these drugs, or about the ways in which behavioral factors themselves may influence the time course and extent of tolerance development (behavioral tolerance). This project will attempt to more fully characterize the importance of behavior itself in the development and loss of tolerance and cross-tolerance to a variety of commonly abused drugs (e. g., amphetamines, barbiturates, narcotics and phencyclidine). The project will focus on schedule-controlled behavior maintained by food or water presentation, and behavior suppressed by aversive events (punishment). We will study the effects of chronically administered drugs on complex, acquired behaviors, with particular reference to similarities and differences among drugs, and to differences in development and loss of tolerance that may depend on the characteristics of the behavior that is studied.